As the demand for fossil fuels continues to grow and fields mature, reservoir characterization has become increasingly important. At the same time, the maturation of many of the world's fields presents new challenges for reservoir characterization. The history of various phases of petroleum geology and reservoir characterization illustrates how these challenges were met in the past, and what new tools and techniques will be emerging in the future. Important past developments include the transition from general petroleum geology to reservoir geology, from disciplinary-focused reservoir description to integrated reservoir characterization, from two-dimensional conceptual mapping of geology to three-dimensional numerical modeling of reservoirs, and from reservoir deterministic analysis to uncertainty analysis. The challenges and perspectives for the future developments in reservoir characterization are also discussed in this chapter.